Layers of lipids in stratum corneum of the skin form a "water barrier" which prevents water loss from the skin. Known classes of stratum corneum lipids include sphingolipids, free fatty acids, sterols and sterol esters, and phospholipids, with sphingolipids being a major component. Sphingolipids, in turn, consist of four major classes of lipids: glycosphingolipids, ceramides, sphingomyelin and total sphingoid base. Ceramides and other sphingolipids play a major role in promoting cell differentiation and, thus, preventing, reducing, or eliminating skin dryness and wrinkles. Although several species of natural ceramides have been identified, these ceramides must be obtained through a lengthy process involving the extraction of ceramides from natural sources. Thus, the availability of natural ceramides is limited and their cost is very high. Several analogs of natural ceramides, known as pseudoceramides, have been synthesized. Pseudoceramides look similar but are not identical to ceramides. Unfortunately, pseudoceramides are still expensive, albeit not as expensive as natural ceramides.
Recent work has shown the ability of cultured keratinocytes to synthesize sphingolipids. Due to the high cost of natural or synthetic sphingolipids, cosmetic compositions which can enhance production of sphingolipids are desirable, in order to minimize or eliminate the need for exogenous application of sphingolipids.
Skin care compositions are known, which include some of the thiol compounds disclosed herein. For example, some thiol compounds have been employed in skin treatment compositions as anti-oxidants. See EP 0 440 398 (Johnson and Johnson) and EP 0 280 606 (L'Oreal). Fahim, U.S. Pat. No. 4,711,780 discloses a composition for epithelial regeneration containing vitamin C, a zinc salt and a sulfur amino acid, such as cystine or cysteine, or glutathione. Schreuder, U.S. Pat. 4,721,705 discloses the use of N-acyl cysteine, or S-acyl-cysteine in compositions for treating sun eczema or dishydrosis of skin. Several thiol compounds have been identified as effective UV light screening agents. See Kahn, Guinter et al. "Ultraviolet Light Protection by Several New Compounds", Arch. Dermatol., Vol. 109, (April 1974) pp. 510-517, and WO 9404129 (Beiersdorf). Hillebrand, U.S. Pat. No. 5,296,500, discloses compositions containing N-acetyl-L-cysteine or derivatives thereof. The compositions are said to efface and prevent wrinkles in mammalian skin.
JP 5339140 discloses a skin cosmetic material containing a mucin and aminoacid, (e.g., serine). The compositions are said to have good moisture retention and improve the wetness of skin. Raaf, U.S. Pat. No. 4,743,442 and Pereira, U.S. Pat. No. 4,981,845 disclose skin care compositions which may contain amino acids, such as serine, cystine, cysteine. Ishida, U.S. Pat. No. 5,141,741, discloses anti-sunburn skin care compositions which may contain vitamins and amino acids as optional ingredients. .alpha.-lipoic acid is mentioned among suitable vitamins; serine and cystine are mentioned among suitable amino acids. Park, U.S. Pat. No. 5,135,741, discloses an anti-perspirant composition containing a compound having a basic nitrogen function, e.g., thiourea or amino acids such as serine.
The art discussed above does not address the need for increasing sphingolipid production in skin and does not envision skin treatment compositions based on a lipid production enhancing system of a thiol or an S-ester or a disulfide and L-serine or N-acetyl-L-serine according to the present invention.
Accordingly, it is an object of the present invention to provide skin treatment compositions for increasing sphingolipid production in mammalian skin.
It is another object of the invention to provide a composition for improving skin condition by improving water barrier performance.
It is another object of the invention to provide a method for treating or preventing the appearance of wrinkled, flaky, aged, photodamaged skin or skin disorders.
These and other objects of the invention will become more apparent from the detailed description and examples that follow.